As a result of the exponential growth of data traffic that is facing today's 3G and 4G operators, international regulatory agencies like the Federal Communications Commission (FCC) and the International Telecommunications Union (ITU) have been urged to create special focus groups such as IMT-2020 in order to establish the technical recommendations and general guidelines to be adopted through the fifth generation (5G) of wireless systems.
Emerging wireless communications standards support the transmission of data rates in the order of multiple Gb/s with a latency of less than 1 millisecond.
The challenging requirements and technical specifications for better performances in 5G systems will require a complete overhaul of existing network architectures.
In order to avoid the cost of fiber optic interconnectivities, it is typically desirable to wirelessly implement fast and point-to-point communications of the backhauling system.
It is also desirable to reduce the energy consumption, the digital signal processing requirements and the cost per unit of access points within a wireless backhauling system to support large-scale deployment and easy penetration of the emerging 5G technology into the market.
Six-port direct conversion receivers have shown promising capabilities since their introduction. Six-port receiver architecture has relatively low costs and a compact size which enables high data rates while requiring less power than conventional heterodyne receivers.
A typical conventional six-port interferometer circuit passes a modulated RF signal through two couplers before being read by a power detector at one of the output ports. Due to the nature of this interferometric scheme, the dynamic range of a typical six-port receiver typically suffers from at least 6 dB loss even when the losses within the circuit substrate are neglected.
Additionally, as operating frequency increases, the losses of six-port receivers also increase, as demonstrated when six-port receivers are operated at the Ka or E-bands of the electromagnetic spectrum. Such losses reduce the dynamic range of the whole receiver and create requirements for the gain of antennas and power amplifiers.